The concept of 'key gangue' and the corresponding hydraulic fracturing technology were proposed for thick coal seams. A hydraulic fracturing test system was developed. The confining pressure ratio plays a crucial role in crack propagation and fracture surface morphology. The results show that the presence of primary fractures in thick coal seams can effectively guide fracture propagation, while horizontal fractures significantly reduce the energy required for fracture initiation and facilitate fracture propagation within the coal seams. Furthermore, the number of gangue layers was found to have a significant impact on the stability of the coal seams, with a higher number of gangue layers leading to increased stability. The application of this technology resulted in a significant reduction in top coal fragmentation, a decrease in the pressure step of the working face, a 5% increase in the recovery of top coal, and a 20% increase in caving efficiency. Received: September 18, 2024; Accepted: March 7, 2025
Gao et al. (Thu,) studied this question.